Ground Fault Interrupters

1/17/2011

While I have heard the story about how the inventor of the ground fault circuit interrupter (GFCI), Charles Dalzial, placed his daughter in a bathtub and threw a toaster that was plugged into a household power supply, into the water while potential investors looked on, just to prove his invention worked; I have not been able to find anything to verify the event’s authenticity. At the same time, I am hesitant to declare this story as merely interesting folklore. It reminds me of the classic tale of William Tell, who, as legend tells (pardon the pun), was a marksman with a cross bow and was forced to draw a quiver and shoot an apple off his son’s head. The legend goes on to tell about the second quiver that William Tell retrieved, which when the evil Gessler made inquiry, William boldly stated that if he missed the apple and hit his son, the second quiver would have been for him.  I wonder if Charles Dalzial devised a contingency for his audience should his demonstration prove to be less than adequate: something that would have kept the world from finding out his invention wasn’t all that it was cracked up to be.        

Legend or not, today we recognize that GFCIs are indeed a vital safety control that protects humans from accidental shock and electrocutions.  Below is a brief explanation of how this device works:

As we can plainly see when handling a typical household electrical plug, there are two vertical slots and then a round hole centered below them. The left slot is slightly larger than the right. This left slot is called “neutral,” the right slot is called “hot” and the hole below them is called “ground.” If an appliance is working properly, all electricity that an appliance uses will flow from hot to neutral. A GFCI monitors the amount of current flowing from hot to neutral and if there is any imbalance, it trips the circuit. This happens because inside the GFI there are two sensing coils that measure the current going out of the black (hot) wire and coming back through the white (neutral) wire. If some of that current going out through the black wire doesn’t come back through the white wire the circuit inside the GFI box senses this “mismatch” and reacts as quickly as one-thirtieth of a second by interrupting (or closing) the electrical flow.  GFCIs are designed to sense current differences as small as 4 or 5 milliamps (fatal events from electrical shock have occurred with as little as 75 milliamps). Should a person (or an object that has the ability to conduct electricity) come in contact with one of the wires, some of the current would be diverted, causing a change in current.

So let’s say you are outside with your power drill and it is raining. You are standing on the ground, and since the drill is wet there is a path from the hot wire inside the drill through you to ground. If electricity flows from hot to ground through you, it could be fatal. The GFCI can sense the current flowing through you because not all of the current is flowing from hot to neutral as it expects — some of it is flowing through you to ground. As soon as the GFCI senses that, it trips the circuit and cuts off the electricity. You might just begin to feel a tingle if you are very sensitive to electricity, but it will not persist long enough to do any harm!!

This does not mean that even when a GFCI is part of the electric circuit, one would be unconditionally protected. Should a person come in contact with both black and white wires at a point after the black wire has left the GFCI, all of the current going out of the GFI through the black wire will go right through you (possibly your heart) and return through the white wire; all this taking place before the GFCI has had the chance to monitor any change in current.

Another type of electrical safety device is the circuit breaker.  While both the GFCI and circuit breaker stop the flow of electricity during conditions where is there is potential danger, they detect very different types of conditions.  Circuit breakers are mechanical devices that control the flow of electrical current through a wire. True to its name, it “breaks” the connection if the current running through the wire in the circuit breaker is more than the wire can handle. A breaker usually has four settings: on, off, tripped and reset. The breaker will display the “tripped” setting when it has automatically turned itself off.

As electricity travels through a wire, it produces heat and a magnetic charge. When the current is at or below the capacity of the wire, the breaker keeps the current flowing. But if the demands on the wire are greater than its capacity, as with a power surge, the wire will overheat. When a wire in an electrical appliance overheats, at best it will melt or burn out or damage that particular appliance. Maybe, the overheated wire will start a fire. Breakers are an essential part of the home’s electrical system, because they prevent fires and electrical malfunctions by stopping the electrical current before the wire overheats. There are a number of different types of circuit breakers, such as bimetallic and electromagnetic. Regardless of the type, circuit breakers are designed to “break” the circuit when too much electricity (greater than what the circuit was designed to handle) at the actual circuit breaker unit.  So, while the GCFI shuts down when it detects an interference within the circuit (which generally indicates a person is having physical contact with the electric line), the circuit breaker shall shut the circuit down when there is too much electricity (current) being generated in the line; regardless of any difference in current between “hot” and “neutral” wires.

Another electrical safety practice is using double-insulated tools. In double insulated tools, exposed metals are separated from electrically live components by supplementary or reinforced insulation, thus protecting the user from any electrical faults.  Double-insulated tools contain two separate insulation systems, a basic and a supplementary system. The two systems must be separated, so that any deteriorating or other problematic factors are never affecting both systems simultaneously. The basic insulation system is applied around the live parts of the tool, where the electrical parts function; separating them from the parts of the tool you touch. The supplementary system adds insulation between the electrical parts and any parts that might cause a hazard to you if there is a breach in the basic insulation system. Therefore, you won’t see metal casings on double-insulated tools. To be advertised as double-insulated, tools must be tested by the Underwriters Laboratory and stamped with the “UL” approval seal.

Although the risk of shock is significantly reduced when using double-insulated tools, some risk remains. When working in damp areas, be aware that moisture can still find its way into the tool’s interior, and if it reaches something electrical, it can shock you when you touch another conductive surface. This risk is heightened using a tool that isn’t double-insulated, however. Be wary also when using power tools in electrically charged areas, because the environment is at a heightened preparation for electric shock already. And if you drop the tool into water, don’t retrieve it without first unplugging it, for the sake of caution.

These safety measures: GCFIs, circuit breakers and double-insulated tools are great devices that have been designed to prevent persons from electrical shock or electrocution. However, it is still up to all us to use electrical appliances correctly and to always use good judgment, for as we can see, these systems are not fail-proof and if used in the wrong setting, can result in serious injury.

Safety saying: If you don’t think it will happen to you, find the person who had it happen to them

If we all did the things we are capable of, we would astound ourselves.
Thomas Edison